It is known to use monomeric acrolein (2-propenal) as a very effective biocide in the treatment of water channels in order to suppress unwanted algae and plant growth. Similarly, it may be used to combat sulphate-reducing bacteria in petroleum exploration.
Until now, no other fields of application have been opened up for the biocidal action of monomeric acrolein in view of its high reactivity. Investigations have shown that acrolein is subject to rapid changes in aqueous systems such as, for example, hydration or polymerisation, depending on the pH (see FIG. 1). Consequently, it has also been impossible hitherto to use acrolein as a preservative with a prolonged effect. Due to its tendency to polymerise spontaneously and possibly in an explosive manner if treated incorrectly, it can be handled only by taking special safety measures. It has a strong irritant effect on the respiratory organs and the eyes. Even in the stabilised form, acrolein may be stored only for a limited period.
It is known to use copolymers of acrolein with formaldehyde, which were prepared by condensation of acrolein and formaldehyde in a molar ratio between 1:1 and 1:10 in the presence of a basic catalyst, as biocides for aqueous systems (DE-B 32 05 487). The known copolymers of acrolein with formaldehyde have the disadvantage that they contain about 15% of free, unreacted formaldehyde.
It is known to use homopolymers of acrolein as biocides (EP-A 0 339 044). Polymerisation is carried out predominantly with radicals. The polyaldehyde structures forming during this process are said to be vehicles of the biocidal action (structural similarity with glutaraldehyde). The formation of free acrolein is not mentioned. The homopolymers of acrolein produced by radical polymerisation have the disadvantage of being insoluble in organic media or in water and, in the form of an aqueous suspension, exhibit only a very low biological activity.
The preparation of polyacroleins described in German patent application P 44 04 404 is problematic because the yields from the reaction of acrolein with NaOH in the aqueous system are only 75-80% of polymer material. Mother liquor and wash water which contain organic substances and must therefore be disposed of at great expense are thus obtained. Recycling is not possible because of the negative effect on the polymer properties. These polymers, too, are virtually insoluble in water.